In Japanese Patent Application Laid-Open Publication No. 2005-169541 (Patent Document 1), there is described a structure of an acceleration sensor in which a MEMS chip having a MEMS formed therein and an IC chip having an IC (Integrated Circuit) formed therein are arranged so as to oppose to each other at a predetermined spacing therebetween. Particularly, in order to achieve both downsizing and thickness-reduction of the acceleration sensor and improvement of a detection sensitivity of the acceleration sensor, the IC chip which electrically processes detection signals from the MEMS chip also functions as a regulation board. In order to prevent electrical contact between the MEMS chip and the IC chip caused by shock from the outside, an insulating layer is formed on the surface of the IC chip that opposes to the MEMS chip. In the acceleration sensor thus formed, the MEMS chip and the IC chip, which are disposed so as to oppose to each other with the predetermined spacing therebetween, are connected to each other by bonding wires, and the MEMS chip and the IC chip configuring the acceleration sensor are hermetically sealed by packaging.
In Japanese Patent Application Laid-Open Publication No. 2004-271312 (Patent Document 2), there is described a capacitor-type semiconductor sensor which mounts a MEMS chip on a circuit chip by using bump electrodes. An object of this technique is to eliminate fluctuations of a parasitic capacitance generated between adjacent bonding wires when the gaps between the bonding wires are narrowed along with increase of the degree of integration in the case where an electrical connection between the MEMS chip and the circuit chip is formed by the bonding wires. In order to achieve this object, the electrical connection between the MEMS chip and the circuit chip is formed by bump electrodes instead of wire bonding. Therefore, the parasitic capacitance generated between the bonding wires can be eliminated, and deterioration of detection accuracy caused along with the fluctuations of the parasitic capacitance can be prevented. Also in this technique, the MEMS chip and the circuit chip are hermetically sealed by a package.
In Japanese Patent Application Laid-Open Publication No. 2005-172690 (Patent Document 3), there is described a hermetic sealing method of a MEMS structure using an anodic bonding of glass substrates and a silicon substrate. Specifically, the MEMS structure is hermetically sealed by anodically bonding between the glass substrates and the silicon substrate under a reduced pressure. Herein, in the anodic bonding, a residual gas generated in the sealed space in which the MEMS structure is disposed can be removed by carrying out heating treatment by a predetermined temperature and time, and the pressure of the sealed space in which the MEMS structure is disposed can be reduced to a state close to vacuum. Thus, without disposing a getter or the like for oxygen absorption in the sealed space in which the MEMS structure is disposed, the pressure of the sealed space can be reduced to the state close to vacuum, a sealing case can be downsized, and also manufacturing steps of the sensor can be simplified, thereby improving production efficiency.